Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.713304
Title: Frequency domain analysis and design of nonlinear systems with application in chemical engineering
Author: Nik Ibrahim, Nik Nor Liyana
ISNI:       0000 0004 6350 4556
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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Abstract:
Frequency domain analysis are widely done in recent years although it is much more complicated compared to the time domain because it can provide a more physical meaningful insight into the system dynamic behaviours such as stability and resonance. Frequency response function (FRF) is the frequency domain representation of linear systems. However, as most of practical engineering systems could not be modelled as linear systems, nonlinear systems analysis becomes an interesting topic to be researched. Output Frequency Response Function (OFRF) is an extension of FRF to the nonlinear systems. The advantage of using the OFRF method is the link between the parameters that define the system nonlinearity and the output frequency response of the system can be observed and understood. This relationship between the parameters that define the system nonlinearity and the output frequency response of the system provides the important basis for the nonlinear system analysis and design in frequency domain. This research is concerned with two major scopes: 1. The development of a more effective method for the determination of OFRF for both single input single output (SISO) and multi input multi output (MIMO) nonlinear systems. • A new numerical method for determining and expressing the OFRF of nonlinear systems using Associated Linear Equations (ALEs) is discovered for SISO nonlinear systems, where this new methodology provided significant improvement and efficiency in determining the OFRF of the nonlinear system. Using the same case study, the number of numerical simulations needed to determine OFRF is less compared to the method in the current literature [46]. The mathematical model used in this new method is nonlinear differential equation (NDE). • However, most of nonlinear engineering systems are MIMO nonlinear systems. Therefore, to make a new contribution to the numerical method in the frequency domain, the new numerical method of determining the OFRF of nonlinear systems using ALEs for SISO nonlinear systems is extended to the MIMO nonlinear systems. Detailed algorithms for the new numerical method are presented and these findings opened a new insight into the understanding of the relationship between the nonlinear parameters and the output of the MIMO nonlinear systems. • The new numerical method of determining and expressing the OFRF of nonlinear systems using ALEs for the SISO nonlinear system and the MIMO nonlinear system were applied to the passive engine mount system and the earthquake engineering. Detailed process of the determination of OFRFs was presented and the OFRF based analysis was done using the OFRF determined to facilitate the design process of the nonlinear systems. These applications show the efficiency of the new numerical method determined in this research. 2. The application of OFRF approach to the analysis of the output frequency response of chemical engineering systems. • The current method in the analysis and design in the frequency domain of nonlinear chemical engineering systems cannot provide an explicit relationship between the nonlinear parameters and the output frequency response function. As the OFRF can solve this problem and provide a new understanding of the nonlinear chemical process, the new numerical method presented in this thesis was applied to the nonlinear non-isothermal continuous stirred tank reactor (CSTR). The technique used to transform the material and energy balance of the system to the NDE model was by using the Taylor series form. Then, from the NDE model, the new numerical method developed in this research was applied and the OFRF of the system was determined. The OFRF provides a good solution to the nonlinear non-isothermal CSTR. The relationship between the nonlinear parameter and the output spectrum of the nonlinear system is analyzed and design of the system can be done from the analysis. As a conclusion, this research contributes new numerical methods in frequency domain analysis. The new numerical methods presented provide new understanding of the relationship between the parameters that described the nonlinearities and the outputs of the system while making the process of OFRF determination more efficient. It has been applied to the analysis and design of nonlinear chemical engineering process system. It helps in the understanding of the nonlinear chemical process identification and revealing the relationship between the system output frequency response and parameters that define the system nonlinearity.
Supervisor: Lang, Zi Qiang Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.713304  DOI: Not available
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